a. Field of the Invention
The present invention relates to a novel method of preparing an alkyl sulfonic acid, and, more particularly, it relates to a novel process of recovering the intended alkyl sulfonic acid from a photosulfoxidation reaction mixture.
B. Description of the Prior Art
The alkyl sulfonic acids popular as surface active agents have usually been prepared by means of photosulfoxidation of an alkane. The conventional method of recovering alkyl sulfonic acids entails very complicated processes in order to obtain the intended product from a reaction mixture: namely, a major portion of the unreacted alkane is separated from the photosulfoxidation reaction mixture by settling; then, said mixture is first heated to evaporate the sulfur dioxide contained therein; subsequently, after concentration of the mixture by heating, the sulfuric acid is separated therefrom by settling; the mixture thus treated is neutralized and thereafter subjected to steam-distillation to separate alkane therefrom, whereby the intended alkyl sulfonic acids are recovered in the form of an alkali salt. Not only that, this method in the prior art involves knotty problems also from the aspect of the thermal efficiency, such as: it is necessary to cool, on the occasion of neutralizing an alkyl sulfonic acid, the reaction mixture concentrated by heating at the time of separating sulfuric acid therefrom; the steam-distillation process following the neutralization process brings about an increase in the viscosity of the reaction mixture as the separation of alkane progresses, making it necessary to heat the mixture again in order to control said viscosity; and so on.